This is a double blind, randomized, placebo-controlled, 2-arm, Phase 2 trial investigating the efficacy and safety of combination therapy of pimasertib plus SAR245409 and pimasertib placebo administered once per day compared to pimasertib administered twice per day plus SAR245409 placebo administered once per day in subjects with previously treated unresectable low-grade serous ovarian or peritoneal carcinoma or serous borderline ovarian or peritoneal tumors.